Loading...
Search for:
wave
0.011 seconds
Total 1385 records
Analysis and simulation of ring resonator silicon electro-optic modulators based on PN junction in reverse bias
, Article Optical Engineering ; Vol. 53, issue. 12 , 2014 ; ISSN: 00913286 ; Akbari, M ; Sharif University of Technology
Abstract
The theory of silicon optical modulators of ring resonators based on PN diode in reverse bias is primarily discussed. It secondarily provides a full-featured simulator to investigate the behavior of such modulators. Wave equation for ring structure will be solved by using the conformal transformation method and the matrix method as it was used to analyze bent planar optical waveguides. Power coupling between ring and straight waveguides will be calculated by coupled theory of nonparallel waveguides based on experimental results. The time response demonstrates the capability of this device to operate correctly at up to 10 Gbs-1 bitrate, and the frequency spectrum analysis of device shows a >...
Impact of loss on the wave dynamics in photonic waveguide lattices
, Article Physical Review Letters ; Vol. 113, Issue. 12 , 2014 ; ISSN: 00319007 ; Weimann, S ; Jafari, K ; Nezhad, M. K ; Langari, A ; Bahrampour, A. R ; Eichelkraut, T ; Mahdavi, S. M ; Szameit, A ; Sharif University of Technology
Abstract
We analyze the impact of loss in lattices of coupled optical waveguides and find that, in such a case, the hopping between adjacent waveguides is necessarily complex. This results not only in a transition of the light spreading from ballistic to diffusive, but also in a new kind of diffraction that is caused by loss dispersion. We prove our theoretical results with experimental observations
Statistical anisotropies in gravitational waves in solid inflation
, Article Journal of Cosmology and Astroparticle Physics ; Vol. 2014,Issue. 9 , 2014 ; ISSN: 14054179 ; Emami, R ; Firouzjahi, H ; Wang, Y ; Sharif University of Technology
Abstract
Solid inflation can support a long period of anisotropic inflation. We calculate the statistical anisotropies in the scalar and tensor power spectra and their cross-correlation in anisotropic solid inflation. The tensor-scalar cross-correlation can either be positive or negative, which impacts the statistical anisotropies of the TT and TB spectra in CMB map more significantly compared with the tensor self-correlation. The tensor power spectrum contains potentially comparable contributions from quadrupole and octopole angular patterns, which is different from the power spectra of scalar, the cross-correlation or the scalar bispectrum, where the quadrupole type statistical anisotropy dominates...
High-performance/low-temperature-processed dye solar cell counter electrodes based on chromium substrates with cube-like morphology
, Article Journal of Power Sources ; Vol. 260 , 2014 , Pages 299-306 ; ISSN: 03787753 ; Taghavinia, N ; Sharif University of Technology
Abstract
There is still an open question of how to prepare high-performance counter electrodes for dye solar cells (DSCs) at room temperature; a requirement for flexible DSCs. Here, we introduce Pt deposited cube-like chromium coating as a low-temperature highly-efficient counter electrode for DSCs. Cr is a chemically stable metal and can be easily electroplated on conductive substrates with high roughness (here ∼160 nm) and cube-like appearance. A cyclic electrochemical deposition method with optimized temperature and number of cycles is used to grow Pt nanoparticles on this surface and charge transfer resistance as low as 0.54 Ω cm2 and 0.27 Ω cm2 were obtained at 40 °C and 55 °C solution...
Numerical modeling of surface reaction kinetics in electrokinetically actuated microfluidic devices
, Article Analytica Chimica Acta ; Vol. 838, issue , August , 2014 , pp. 64-75 ; ISSN: 00032670 ; Amini, Y ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
Abstract
We outline a comprehensive numerical procedure for modeling of species transport and surface reaction kinetics in electrokinetically actuated microfluidic devices of rectangular cross section. Our results confirm the findings of previous simplified approaches that a concentration wave is created for sufficiently long microreactors. An analytical solution, developed for the wave propagation speed, shows that, when normalizing with the fluid mean velocity, it becomes a function of three parameters comprising the channel aspect ratio, the relative adsorption capacity, and the kinetic equilibrium constant. Our studies also reveal that the reactor geometry idealized as a slit, instead of a...
Theoretical considerations in designing ultra-high speed all-optical clock recovery using fiber optical parametric amplifiers
, Article Journal of Lightwave Technology ; Vol. 32, issue. 15 , August , 2014 , pp. 2678-2689 ; ISSN: 07338724 ; Salehi, J. A ; Sharif University of Technology
Abstract
In this paper, a new all-optical phase-locked loop (OPLL) in a TDM system is proposed and analyzed. The scheme relies on using fiber optical parametric amplifier (FOPA) device models and theories. In the proposed OPLL, the local clock pulse stream and the received data signal pulses are fed into the FOPA as its pump and amplified signals, respectively. The power of the resulting, relatively, strong idler signal depends on the phase difference between the local clock and the received data signal pulses, and it is used to reveal the OPLL's error signal. We characterize the mathematical structure of the proposed OPLL and identify its three intrinsic sources of phase noises namely, randomness of...
A circuit model for analysis of metal-insulator-metal plasmonic complementary split-ring resonators
, Article Journal of Lightwave Technology ; Vol. 32, issue. 15 , August , 2014 , pp. 2659-2665 ; ISSN: 07338724 ; Eshaghian, A ; Mehrany, K ; Sharif University of Technology
Abstract
A circuit model based on the transmission line theory is proposed to analyze the recently introduced metal-insulator-metal (MIM) complementary split-ring resonators (CSRRs). It is shown that integer and noninteger modes of CSRRs can be characterized by transmission line models with short- and open-circuited terminals. The proposed circuit model is then extended to incorporate side-coupling effects between the CSRRs and straight MIM waveguides. Thereby, simple closed-form expressions are provided for the coupling quality factor. It is shown that waveguide resonator structures based on CSRRs at specific resonance frequency and bandwidth can be smaller than waveguide resonator structures based...
Investigating the possibility of Sonofusion in Deuterated acetone
, Article International Journal of Hydrogen Energy ; Vol. 39, issue. 21 , July , 2014 , pp. 11328-11335 ; ISSN: 03603199 ; Sadighi-Bonabi, R ; Sharif University of Technology
Abstract
In this article, energetic implosion of a single vapor bubble induced by a standing acoustic wave is theoretically studied and the Sonoluminescing bubble parameters involved in Sonofusion in Deuterated acetone (C3D 6O) are investigated. Parameters such as radius, wall velocity, interior temperature and pressure of the bubble influenced by various driving pressure amplitudes in Deuterated acetone at ∼0 °C are investigated. Based on the obtained results, the possibility of thermonuclear fusion inside imploding cavitation bubbles is discussed. The interior pressure of C 3D6O vapor bubbles at the collapse time is extremely high and the increase of the pressure amplitude increases the pressure...
Interaction of 3D dewetting nanodroplets on homogeneous and chemically heterogeneous substrates
, Article Journal of Physics Condensed Matter ; Vol. 26, Issue. 22 , 2014 ; ISSN: 09538984 ; Moosavi, A ; Sharif University of Technology
Abstract
Long-time interaction of dewetting nanodroplets is investigated using a long-wave approximation method. Although three-dimensional (3D) droplets evolution dynamics exhibits qualitative behavior analogous to two-dimensional (2D) dynamics, there is an extensive quantitative difference between them. 3D dynamics is substantially faster than 2D dynamics. This can be related to the larger curvature and, as a consequence, the larger Laplace pressure difference between the droplets in 3D systems. The influence of various chemical heterogeneities on the behavior of droplets has also been studied. In the case of gradient surfaces, it is shown how the gradient direction could change the dynamics. For a...
Investigating the effects of vibration method on ultrasonic-assisted drilling of Al/SiCp metal matrix composites
, Article Robotics and Computer-Integrated Manufacturing ; Vol. 30, issue. 3 , 2014 , Pages 344-350 ; ISSN: 07365845 ; Akbari, J ; Yousefi, R ; Rahi, A ; Nick, M. G ; Sharif University of Technology
Abstract
Preciseness and finished surface quality are the significant factors of final products, especially in a number of drilling processes. Burr is usually considered a negative outcome in assembly procedures. One way to reduce or remove burr and improve surface roughness in metal cutting is to employ ultrasonic vibration in the drilling process. In this paper, the effects of ultrasonic vibration on burr size reduction, drilling force and surface roughness with two different vibration systems are investigated. To this end, two vibration structures were built, one to excite the workpiece (the workpiece vibration system) and the other to vibrate the tool (the tool vibration system). Besides, the...
An accurate semi-analytical method for an arbitrarily oriented edge or interior crack in an anisotropic homogeneous elastic solid
, Article European Journal of Mechanics, A/Solids ; Vol. 45 , May , 2014 , pp. 133-142 ; ISSN: 09977538 ; Shodja, H. M ; Sharif University of Technology
Abstract
In this work, a general semi-analytical method for the determination of the elastic fields within an anisotropic homogeneous elastic solid with an inclined edge or interior crack is developed. In this method, the displacement field is represented as a sum of a function and a finite series of functions with unknown coefficients. The functions are constructed in such a way that all the essential homogeneous and inhomogeneous boundary conditions are satisfied exactly and, moreover, the displacement discontinuity across the crack faces as well as the exact singular behaviour of the stress field at the crack-tip are captured. The unknown coefficients are determined by utilizing the principle of...
Theoretical and experimental broadband tissue-equivalent phantoms at microwave and millimetre-wave frequencies
, Article Electronics Letters ; Vol. 50, issue. 8 , April , 2014 , p. 618-620 ; ISSN: 00135194 ; Saviz, M ; Shishegar, A. A ; Sharif University of Technology
Abstract
Several phantoms have been fabricated for reflection measurements from human tissues in the range of 26.5-40 GHz. For the first time, a novel composition is introduced for fabrication of low-cost simple tissue-equivalent phantoms. The effective medium theory is applied to estimate the dielectric properties of phantoms consisting of polyethylene (PE) powder and the results are verified by dielectric properties measurement on the proposed phantoms. It is shown that mixing theory can estimate the dielectric properties of the PE-based phantoms with minimum error. Therefore, the amount of the ingredients can be estimated theoretically
An exploration in acoustic radiation force experienced by cylindrical shells via resonance scattering theory
, Article Ultrasonics ; Vol. 54, issue. 4 , April , 2014 , pp. 971-980 ; ISSN: 0041624X ; Behzad, M ; Sharif University of Technology
Abstract
In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each...
Effect of thermal wave propagation on thermoelastic behavior of functionally graded materials in a slab symmetrically surface heated using analytical modeling
, Article Composites Part B: Engineering ; Vol. 60 , 2014 , pp. 413-422 ; ISSN: 13598368 ; Ahmadian, M. T ; Taati, E ; Sharif University of Technology
Abstract
Design and development of FGMs as the heat treatable materials for high-temperature environments with thermal protection require understanding of exact temperature and thermal stress distribution in the transient state. This information is primary tool in the design and optimization of the devices for failure prevention. Frequently FGMs are used in many applications that presumably produce thermal energy transport via wave propagation. In this study, transient non-Fourier temperature and associated thermal stresses in a functionally graded slab symmetrically heated on both sides are determined. Hyperbolic heat conduction equation in terms of heat flux is used for obtaining temperature...
Molecular dynamics simulation of orientation dependency in the shock-induced phase transition of C60 fullerene single crystals into amorphous diamond
, Article Phase Transitions ; Vol. 87, Issue. 3 , 2014 , Pages 271-285 ; ISSN: 01411594 ; Naghdabadi, R ; Sharif University of Technology
Abstract
A molecular dynamics simulation of the shock-wave propagation in the face-centered cubic (FCC) structured C60 fullerene along the <100>, <110> and <111> crystallographic directions is performed. For this purpose, the response of the material under different shock-wave loadings is studied through Hugoniot curves. Three regimes of the material behavior have been observed from fully elastic to elastic-plastic to plastic. The Hugoniot elastic limit and the phase transition are also investigated along different crystallographic directions. It is shown that the shock wave travels faster along the <110> and <111> directions than in the <100> direction in the material. Comparing the results with the...
Axial-torsional vibrations of rotating pretwisted thin walled composite beams
, Article International Journal of Mechanical Sciences ; Vol. 80 , 2014 , pp. 93-101 ; ISSN: 00207403 ; Haddadpour, H ; Sharif University of Technology
Abstract
Axial-torsional vibrations of rotating pretwisted thin-walled composite box beams exhibiting primary and secondary warping are investigated. Considering the nonlinear strain-displacement relations, the coupled nonlinear axial-torsional equations of motion are derived using Hamilton's principle. Ignoring the axial inertia term leads to differential equation of motion in terms of elastic torsion in the case of axially immovable beams. Centrifugal load in the presence of material anisotropy and pretwist angle leads to an induced static torque. The nonlinear equation should be linearized about the corresponding equilibrium state to obtain the linear differential equation of motion. Extended...
Circuit-breaker automated failure tracking based on coil current signature
, Article IEEE Transactions on Power Delivery ; Vol. 29, issue. 1 , February , 2014 , pp. 283-290 ; ISSN: 08858977 ; Vakilian, M ; Niayesh, K ; Lehtonen, M ; Sharif University of Technology
Abstract
The online condition assessment of circuit breakers (CBs) has been increasingly requested by power utilities in recent years. Trip and close coil current (CC) signature is an effective and noninvasive parameter in CB online condition monitoring. This paper gives an insight into the impacts of the various failures on the coil current waveform, as well as on the CB operation time. The failures and their causes are categorized based on the outcome of these investigations. Finally, a new algorithm using trip/close CC is proposed to detect the mode and cause of CB incipient failures. In this study, the CC patterns are acquired by measurements carried out on (healthy and faulty) CBs of 72.5-kV and...
A technique for detection of interfacial waves forming a two-dimensional pattern
, Article Fluid Dynamics Research ; Vol. 46, issue. 1 , 2014 ; ISSN: 01695983 ; Fazeli M ; Jamali, M ; Sharif University of Technology
Abstract
In this paper, we consider resonant interaction between a surface wave and sub-harmonic interfacial waves forming a two-dimensional pattern at the interface between two fluid layers. The resulting interfacial pattern changes both in time and space. An image processing technique is proposed to extract information about the evolution of the component interfacial waves in a wave flume. The technique proved to give accurate and consistent results when applied to different stages of the interaction. The experimental measurements were used to verify the theoretical predictions. The method can be used for detection of some other wave motions
Requirements for soil-specific correlation between shear wave velocity and liquefaction resistance of sands
, Article Soil Dynamics and Earthquake Engineering ; Vol. 57, issue , 2014 , pp. 152-163 ; ISSN: 02677261 ; Akbari Paydar, N ; Sharif University of Technology
Abstract
The application of the simplified method for evaluating the liquefaction potential based on shear wave velocity measurements has increased substantially due to its advantages, especially for microzonation of liquefaction potential. In the simplified method, a curve is proposed to correlate the cyclic resistance ratio (CRR) with overburden stress-corrected shear wave velocity (Vs1). However, the uniqueness of this curve for all types of soils is questionable. The objective of this research is to study whether the correlation between CRR and Vs1 is unique or not. Besides, the necessity of developing the soil-specific correlations is also investigated. Based on laboratory test data, a new...
Assessment of offshore structures under extreme wave conditions by Modified Endurance Wave Analysis
, Article Marine Structures ; Volume 39 , December , 2014 , Pages 50-69 ; ISSN: 09518339 ; Mohajernassab, S ; Seif, M. S ; Tabeshpour, M. R ; Mehdigholi, H ; Sharif University of Technology
Abstract
Recently, various approaches have been introduced to estimate the response of offshore structures in different sea states by stepwisely intensifying records. In this article, a more practical approach entitled Modified Endurance Wave Analysis (MEWA) considering the random and probabilistic nature of wave loading and utilizing optimal time duration is introduced. Generation procedure of this approach is described based on two practical wave theories: random and constrained new-wave. In addition, assessment of a simplified model representing a typical fixed offshore platform under extreme wave conditions in the Persian Gulf is performed making use of MEWA. A comparative analysis has been also...